According to Humphris and Scott (JCS Perkins II, pp 923-835, 1973) the mechanism for prevention of oxidation of hydrocarbons in air by oxidation inhibitors involves three stages. The first stage involves competition for dissolved oxygen molecules wherein a dissolved addition agent has the ability to utilize dissolved oxygen more effectively than the hydrocarbon in its formation of hydroperoxides as a first product. The second stage involves decomposition of said hydroperoxides faster than the thermal decomposition. Since hydroperoxide thermal decomposition can provide reactive radicals which are oxidation propagators, the dissolved addition agent should provide a chain-transfer capacity which terminates reactive radicals into non-propagating species.
Those three effects have been, in general, accomplished by the use of two or more hydrocarbon-soluble addition agents each performing to its own capacity and advantage in a concerted, compatible effort to make up for the weakness of the other addition agents present. For example, a hindered phenol is used in combination with a phosphosulfurized hydrocarbon (an acidic product of the reaction of P.sub.2 S.sub.5 with a medium to long chain mono-olefin) or salt thereof. At times the combination of addition agents in hydrocarbons (distillate fuels and lubricant oils) have been quite subtle in their combined effects. While one or two might be recognized as oxidation inhibitors, each may totally lack one of the three above activities, for example chain-transfer. However, another type of addition agent, for example, an anti-rust, anti-corrosion or anti-wear or detergent agent may also have some chain-transfer capacity and terminate reactive radicals into non-propagating species. Such subtly active compounds used in the past were metal-containing compounds. Now the trend is to decrease at least to a minimum, if not entirely, the use of ash deposit forming metal-containing addition agents for distillate fuels (gasoline, diesel fuel, heating oils) and lubricant oils. The search for so-called ash-free hydrocarbon addition agents since the early 1960's has brought to light the exacting requirements for necessary effects by addition agents. For example, the early use of "ash-free" detergent addition agents such as amine derivatives (amides, imides and amidines) of an organic carboxylic acid (e.g., oil-soluble, long chain-containing succinnic acid or anhydride), or a Mannich base derived from the condensation of a hydrocarbon-soluble alkylkphenol, an aldehyde and an amine brought with it the unexpected "thermal thickening" which was really a result of hydrocarbon oxidation. Such thickening was most pronounced in crankcase lubricant oils where the lubricant oil formulation would suddenly increase in viscosity and take on a gel-like or mayonnaise-like appearance.
So far the trend for using an "ash-free" oxidation inhibitor has included the use of a known "ash-free" ion-radical catalyst for hydroperoxide decomposition. Hindered phenols or phosphites thereof, which are of the ash-free type, are used for their in situ ion-radical formation for catalytically decomposition of hydroperoxide.
We have now discovered a single additive species which possesses the three before-mentioned activities of fast utilization of oxygen dissolved in hydrocarbon, exert some catalytic activity for hydroperoxide decomposition and chain-transfer to terminate reactive radicals to non-propagating species. We have not in our search of the pertinent art found any reference to said additive species either per se or its use in hydrocarbons to suppress their oxidation. Hence we believe the inventive additive species to be a novel composition of matter, its preparation to be novel, and its use as a hydrocarbon oxidation inhibiting agent as well to be novel.